Syringes are often used to deliver fluids (i.e. liquids and gases). These devices generally comprise a reciprocating pump utilizing a plunger or piston fitted within a cylindrical body or barrel. As the plunger is biased within the barrel, fluid may be drawn into the barrel or expelled therefrom. An open end of a syringe may be fitted with a needle, nozzle, or other interface depending on a desired application. Syringes are frequently used in clinical medicine to administer injections, infuse intravenous pharmaceutical products into the bloodstream, apply compounds such as glue or lubricant, and to draw and measure liquids. Stoppers or caps are widely used in many industries, including the medical industry, for selectively sealing or closing containers such as vials.
Pharmaceutical products or solutions often have characteristics that present an increased likelihood of unwanted interaction between the product and certain types of materials. For example, polymer materials, such as rubber used to make plungers used in syringe assemblies and stoppers used to close medical containers, are subject to leakage or chemical breakdown which can contaminate the solution. In order to prevent these chemical reactions between the polymer material and the solution, chemically inert barrier layers or films, such as those formed from fluoropolymer materials, are provided on surfaces of the components that will be exposed to the solution.
Particularly in the field of syringe plungers, the addition of this barrier material or layer complicates the manufacturing process. Moreover, in order to create a reliable barrier, plunger designs have required relatively thick barrier material layers. These drawbacks significantly increase manufacturing costs. More specifically, and referring generally to FIG. 1, an exemplary plunger 2 of the prior art is shown. Plunger 2 comprises a first end or face 3 which is exposed to a substance (e.g., fluid or solution) when installed within a syringe. Plunger 2 terminates at a second end 7 configured to attach to, for example, a moveable plunger rod for selectively biasing plunger 2 within a barrel of the syringe. In order to isolate the body of plunger 2 from a solution contained within a syringe, a barrier layer or barrier film must be formed over face 3. In order to ensure complete isolation between the body of plunger 2 and the solution, this layer must be applied over a first sealing rib 8 and up to or beyond a point of tangency or contact T with an internal barrel wall of a syringe. In order to reliably form this layer around at least a portion of sealing rib 8, a two-step over molding process for manufacturing plunger 2 is typically employed. In a first step, a first portion 4 of plunger 2 is molded and a barrier material subsequently formed over face 3, as well as at least a portion of sealing rib 8. Forming the barrier layer over the radiuses of sealing rib 8 commonly leads to the formation of undesirable wrinkles and/or tears in the layer that may result in capillary fissures. Moreover, ensuring uninterrupted and uniform coverage of this layer typically requires a relatively thick (e.g., five thousands of an inch), and therefore more expensive, layer of barrier material. Once formed, a second portion 6 of plunger 2 is molded over and joined with first portion 4, creating a monolithic body. This two-step process is time consuming and expensive. Many of the above drawbacks also apply to stoppers or sealing devices which utilize barrier layers or films.
Alternative designs and manufacturing processes for these items are desired.